Characterization of a Novel Marine Origin Aerobic Nitrifying–denitrifying Bacterium Isolated from Shrimp Culture Ponds

A novel marine origin Bacillus subtilis strain H1 isolated from a shrimp culture pond effectively removed NH4+-N, NO2--N and NO3--N, with a maximum ammonium, nitrite and nitrate removal rate of 2.35 mg NH4+-N L-1 hr(-1) per OD, 9.64 mg NO2--N L-1 hr(-1) per OD and 0.75 mg NO3--N L-1 hr(-1) respectively. The gas chromatography-isotope ratio mass spectrometry results indicated that N2O was emitted when (NH4Cl)-N-15, (NaNO2)-N-15 or (NaNO3)-N-15 was used. Additionally, N-2 was also produced when (NaNO2)-N-15 was used. Single-factor experiments suggested that the optimal conditions for NH4+-N and NO2--N removal were glucose as a carbon source, C/N 15, initial pH 7.5, 30 g/L NaCl, 28 degrees C and a shaking speed of 160 rpm. Orthogonal tests showed that the optimal conditions for NH4+-N removal were C/N 15, pH 9, 10 g/L NaCl and shaking speed 160 rpm when ammonium chloride was used as the substrate. The optimal conditions for NO2--N removal were C/N 10, pH 6, 10 g/L NaCl and a shaking speed of 160 rpm when sodium nitrite was used as the substrate. In summary, B. subtilis strain H1 had highly efficient aerobic nitrifying-denitrifying ability and high adaptability, suggesting that it is potentially valuable to marine aquaculture.